Adjustable transformer, preferably for current supply of x-ray installations



Nbv. 4, 1958 OLE LUTZ HOPPERMANN 2 859,421

ADJUSTABLE TRANSFORMER, PREFEIRABLY FOR CURRENT SUPPLY OF X-RAYINSTALLATIONS Filed Jan. 30, 1957 INVENTOR.

4o O1: Lul'z H rper/ 4.97;

A BY L United States Patent O ADJUSTABLE TRANSFORMER, PREFERABLY FORCURRENT SUPPLY OF X-RAY INSTALLATIONS Ole Liitz Hoppermann,Charlottenlund, Denmark, assignor to Holger Andreasen, Copenhagen,Denmark, aDanish firm Application January 30, 1957, Serial No. 637,212 2Claims. (Cl. 336147) 'The invention relates to an adjustabletransformer, preferably for current supply of X-ray installations andfor a minimum line voltage, for example 110 volts, and at least onehigher line voltage, for example 220, 380, 440 and 480 volts, and withfixed or adjustable taps, partly for means, for example for othertransformers, which feed the X-ray tube with filament current and hightension, partly for the auxiliary devices of the installation such asrelays and oil pump, and of the kind having an inner and an outerwinding, both substantially uniformly distributed on an annular ironcore, and in which the outer winding is accessible by means of at leastone adjustable tap, for example a sliding contact resting against astripped part of the outer winding or against a number of tapsdistributed along this winding, the outer winding being by means of theother tap divided into two winding sections of which the former has asubstantially larger number of windings than the other winding section.

Transformers of the aforesaid kind are known and constitute a furtherdevelopment of the ordinary, known auto-transformers which have onewinding only, uniformly distributed along the circumference of the ironcore, and all its windings are accessible by means of a sliding contactresting against a stripped part of all the windings. It will beappreciated that if the outer terminals of the winding are connected toa line voltage, for example of 220 volts, the whole winding will act asan exciting winding, and the core will be uniformly energized along itswhole circumference, and between the zero terminal of the winding andthe sliding contact it will be possible to collect a variable voltagewhich in accordance with the position of the sliding contact may bevaried approximately continuously from to 220 volts. If, on the otherhand, the auto-transformer is to be used in combination with a linevoltage of 110 volts, the said voltage is connected between one outerend of the winding and a central tap, and the winding half locatedbetween these will energize the corresponding half of the core moreintensely than the other half of the core. The voltage collected betweenthe zero terminal of the winding and the sliding contact will inthatcase vary both in regard to intensity and in regard to shape ofcurve.

In extreme cases the voltage curve will reach a peak at the middle ofeach half cycle, which involves partly that the transformer yields alower output then if the voltage curve was sinusoidal, and partly thatsuch peaks may involve breakdown or puncture either in the transformerproper or in its connected members and devices.

In the known transformers of the aforesaid kind the inner and the outerwinding are generally connected in series, and the outer winding isprovided with a tap for connection to the lowest line voltage, forexample 100 volts. Since it is generally desirable to have a possibilityofregulating the collected voltage from abt. 70 to 220 volts, the tapfor the lowest line voltage is not located at the point where the innerand the outer windings are joined, but in such manner that the outerwinding is divided into two winding sections, of which the former has anumber of findings substantially larger than the other winding section.The exciting winding for the transformer will, when connected to 110volts line voltage, consist of the whole inner winding plus the otherWinding section of the outer winding. Such part of the core as islocated in the said other winding section is thus subjected to a moreintense magnetization that the remaining part of the core, wherebysimilar phenomena in the shape of a distorted curve shape arise asmentioned above.

In other embodiments of known transformers of the aforesaid kind thereis placed a so-called pre-coil at a limited area of the circumference ofthe annular iron core, preferably on the outer side of the inner and theouter winding. The said pre-coil is in series with the outer winding andis used when the transformer is to be connected to voltages higher than220 volts, for example line voltages 380, 440 and 480 volts. Such aconcentration of the exciting winding will likewise involve an irregularmagnetization of the iron core and similar phenomena as mentioned above.In addition, the irregular shape of the divided winding and the pre-coilrequires relatively large space, which again involves that thetransformer has to be of larger dimensions than is desirable.

It is the object of the invention to devise the construction of anadjustable transformer of the aforesaid kind having none of the saiddrawbacks, and an essential feature of a transformer according to theinvention is that the second winding section consists of a blindlyterminated winding projecting from the other tap, the inner windinghaving a number p+1 winding sections the ends of which lead to outerterminals and of which at least the winding sections p each have anumber n of turns equal to the number of turns in the first windingsection of the outer winding, whereas a winding section number p+l islocated at one end of the inner winding and has a number of turns equalton times the ratio between the difference of the two highest linevoltages and the lowest line voltage.

As a result, the transformer may by a simple changeover andinterconnection of the inner and the outer windings be adapted forconnection both to the lowest line voltage of volts and to the higherline voltages of 220, 440 and 480 volts, and as a further result theexciting winding may in each of the cases mentioned be distributedsubstantially uniformly over the entire circumference of the iron core.

The invention will now be further described with reference to thedrawing, in which Figure 1 is a diagrammatic representation of anembodiment of an adjustable transformer according to the invention, inwhich the two windings of the transformer for the sake of clarity areshown as being arranged on either side of the symbol for the annulariron core of the transformer, whereas, in reality, they are disposedaround the said core, one winding close other winding on top of thefirst one.

Figures 2-5 are diagrammatical representations of other embodiments ofthe adjustable transformer according to the invention.

Figure 1 shows an adjustable transformer consisting of an inner winding1 and an outer winding 2, both substantially uniformly distributed on anannular iron core 3, the outer winding being accessible by means of atleast one adjustable tap 4 which may be a sliding contact or a carbonroller resting in contact with a stripped part or a number of tapsdistributed along the circumference of the outer winding. One end 5 ofthe inner winding is connected to a zero terminal 6 for the line voltageand the other end 7 is connected to a terminal 8 for the lowest linevoltage, which, for instance, may be volts, and

to the iron core and the located between one end 11 of the Outerwindingand. 5

the other tap 9 and into a second winding section, 12 lo? cated betweenthe other tap 9 and the'other andv 1330f the.

outer winding. The one end 11 of the: outer wind ngi passed to. aterminal 14 which 18 .41: Whenth trans;

former is to be connected to a higher line voltage,,.for' The voltagerangefrorn which cur rent is to. be collected between the zero terminal6, andv example 220 volts.

the sliding contact 4, which is connected to a tap terminal 15, rangesnormally inthe installatiQns for which the transformer is preferablyintended, for exampleaX-ray installations, between 70 and 220 volts, anda range of 701-,10 volts can therefore be; collected when the slidingcontact 4. rests against the second winding section 12, whereas currentmay be collected from the range of 110- 220 volts when the slidingcontact rests, against the first winding section 10. I

When the transformer is connected to the lowest line voltage, forexample, 110: volts, its exciting winding will consist, of the entire,inner winding 1, and since the latter is uniformly distributed along thecircumference of the iron; core 3, the core will. be uniformly energizedalong this entirecircumference. If the transformer is connected to thehigher line voltage, for example 220 volts, the exciting Winding willconsist of both the inner wind, ing 1 and the first winding section, 10of the'outer winding, whereas the second winding section 12 will not beincorporated in the exciting winding. The magnetization'of theiron corewill in that case not be so uniformly distributed over, the,circumference of the iron core as in the first mentioned case, but it isonly a fraction, viz. or about 18% of the circumference thatwill bemagnetized by half the magnetizing power in proportion to the remainingpart of the winding, and this difference of 9% in the magnetization hasbeen found not to influence the curve shape of the collected voltages toany appreciable extent. This proportionis at any rate substantially morefavourable than in the known transformers, which are distinguished fromthat disclosed thereby that connection between the terminals 7 and 9 isdispensed with andsubstituted by aconnectionbetween the terminals7ia1j1d: 1 3; a-line voltage of 110 volts being in that case suppliedacross the terminal 9. The last mentioned methodof' connection has .theresult that when the known transformers are connected to. a voltage of110 volts between the terminals 6 and 9, 1.8% of the circumference ofthe iron core will not be subjected to any magnetizing power at all,which involves such an uneven distribution of the magnetization that itproduces a material distortion of the curveshape'of the voltagecollected.

The voltage necessary for the auxiliary devices of the. X-rayinstallation, such as relays and oil pump, iscollected either across theterminals 5 and 7, if 110 volts is desired, or across the terminals 5,and 11, if 220-volts. is desired for this purpose, and thesaidterminals may be. connected to special connecting terminals, for theauxiliary devices, for example, asindicated at the terminals 16 and 17.In the embodiment of the transformer according to the invention as shownin Figure. lthe innerwinding 1 has a number of p=3 winding sectionstheendsof which are connected t theterminal 5. andav terminal 18,

respectively, terminals 191. and.20 and a terminal 2 1 -and the terminal7, a fourth windingsection, a,p.+.'1t,-h-, which exists in the realtransformer, being omitted for the sake,

of clarity, whereas the said, winding sectioninctheem: bodiment of thetransformer accordingtoithe. invention as shown in Figure 4 is disposedatthe one end of-the inner winding and has a number of .turns determinedby the ratio betweenthe difference of the two highest line voltages andthe lowest-line voltage, andthe said winding section begins at the outerterminal 7 of No. p winding Section and is provided with a free endterminal 22. No. p+1 winding section has relatively few turns, forexample n or n, n being the number of turns in the first part 10 of theouter winding, and it is therefore of minor importance to themagnetization of the core whether this section is incorporated in theexciting winding or not, since it is only excluded when all the otherexciting winding receive current, and the alternation will thereforeonly amount to that is 9%.

With the three winding sections connected in parallel and the terminals5, 19, and 21 being interconnected and connected to the line terminal 6,and the terminals 7,

- 18 and 20 being interconnected and connected to the line terminal 8,while the tap 9 is simultaneously connected to the terminal 5, it ispossible to obtain as shown in Figure 2 that the transformer can be usedfor the lowest line voltage, for example 110 volts and with tapping for22 0.volts between the terminals 17 and 16, of which the latter isconnected to the terminal 7 or the terminal 18. The variable voltage-220 volts may as mentioned above be collected between the one end 11-of the outer winding, or its outer terminal 14, andthe adjustable tap 4or its outer terminal 15. In this combination the exciting windingconsists of the three winding sections of the inner winding connected inparallel, and since these sections, apart from No. p+1 winding sectionwhich is omitted; from Figure. 2 are uniformly distributed along thecircumference of the core, the core will be substantially uniformlyenergized along its entire circumference.

The adjustable transformer shown in Figure 2 may also be supplied withcurrent from a 220 volts line if this is connected to the outer.terminals 8 and 14, which does not bring about any change of conditions,neither in regard to the voltages collected across the terminals 16, 17

and 14, 15 or in regard to the magnetization of the iron core.

If, on the other hand, the transformer is to be used for. alinevoltageof.440 volts, the three winding sections of the inner winding areconnected in series as shown in Figure 3, and this does not bring aboutany change of conditions in regard to the voltages collected and themagnetization.

In the embodiment of the transformer as shown in Figure. 4 the thirdwinding section 21, 7 of the inner winding of the transformer isprovided in a manner known per se with a tap 23 dividing the saidwinding section in the ratio 5:6 and lying nearest the terminal 21. Thetap 23 is connected to an outer terminal 24, and the free end terminal22 of winding section No. 2+1 is passed to another outer terminal 25.The transformer may thereby be connected to 380 volts line Voltagebetween the outer terminals 14 and 24, 440 volts line voltage betweenthe outer terminals 14 and 8 and 480 volts line voltage between theouter terminals 14 and 25.

'In an embodiment of the transformer according to the invention thefirst winding section of the outer winding is provided with an extraturn 26 projecting from the end 11 of the outer winding remote from theother tap. Resting in contact with the windings near the said other tap9 and near the said end 11 of the outer winding are other slidingcontacts 27, 28 which contact stripped parts of the windings of theouter winding and are mechanically coupled in such manner that they mayturn simultaneously in the same direction in relation to thecircumference of the outer winding about such axis of symmetry of theiron core as is perpendicular to the plane of movement of the slidingcontacts.

As a result, small variations in the nominal value of the line voltagessupplied to the transformer may be equalised continuously, since asimultaneous turning of the sliding contacts 27, 28 has the etfect thatthe number of turns in the outer winding between the said slidingcontacts is kept constant, whereasthe absolute voltage for the contactpoint of the one slidingcontact with, the outer winding may be alteredin relation to the zero point of the transformer. A special advantageobtained simultaneously is compensation on all voltages collected fromthe transformer at the same percentage value. In the known transformerssuch a compensation for variations from the nominal line voltages canonly be made stepwise and furthermore with the disadvantage that thepercentage alterations become unnecessarily high at the low linevoltages and unjustifiably small at the high line voltages. Themechanical coupling of the sliding contacts 27, 28 may, for example asshown in Figure 4, be effected by attaching the sliding contacts to twoarms 29, 30 emanating from a shaft 31 mounted in the axis of symmetry ofthe iron core, the said arms being coupled together so as to form anangle to each other by means of a member 32 and in such manner thatthere are a number of 11 Windings between their points of contact withthe outer windmg.

The embodiment of the transformer according to the invention as shown inFigure 5 has a number of p-{-1=5 winding sections in the inner winding,that is, four uniform windings disposed respectively between theterminal 5 and a terminal 35, terminals 36, 33 and 34, 37 and a terminal38 and the terminal 7. The transformer may be supplied with currenteither from the lowest line voltage, for example 110 volts, thereby thatthe one end 11 of the outer winding across its terminal 14 and thesliding roll 27 across its outer terminal 39 is connected to the Zeroterminal and the 110 volts terminal of the line voltage, respectively.The winding sections are connected in series by pairs and the two pairsare connected in parallel when the transformer is supplied with currentfrom a 110 volts line. -If it is desired to supply the transformer withcurrent from a 220 volts line, the said voltage is fed through outerterminals 40, 41 leading to terminals 5 and 7, respectively.

It will be appreciated that the transformer disclosed in Figure 5 may beswitched for use at line voltages of 380, 440 and 480 volts when allfour winding sections are connected in series and the terminals 22 and 7the tap 23 are connected to outer terminals for 480, 440 and 380 voltsline voltage, respectively..

It will also be appreciated that the transformer disclosed in Figure 5can be switched for use at a line voltage of 110 volts supplied at theouter terminals 40 and 41 when the p winding sections of the innerwinding are connected in parallel. The transformer consists in this caseof four uniform winding sections plus winding section No. 12-1-1 and theouter winding which may be wound on top of the five inner windings,which, since all of them are incorporated in the exciting winding whenthe transformer is operating, may be either wound in such manner thateach covers 90 of the circumference of the core or in such manner thateach covers 360 of the circumference of the core; in the last-mentionedcase they are placed in four concentric layers. In this case winding No.p+1 is disregarded; the importance of this winding to the magnetizationis of substantially less value, and it may be dispensed with altogetherif the transformer is solely to be used for voltages which are aninteger multiple of the lowest line voltage, for example 110, 220 and440 voltsv If for reasons of safety it is a requirement that none of theoutgoing wires of the transformer have more than 55 volts in relation toearth, the outer winding in the last-mentioned embodiment of thetransformer may be connected to earth at its central point between theterminals 9 and 11.

Although only special embodiments of the adjustable transformeraccording to the invention are described in the foregoing, theprotection should not be limited to the said embodiments, but only belimited by the claims.

What I claim and desire to secure by Letters Patent is:

1. An adjustable transformer, preferably for current supply of X-rayinstallations and for a minimum line voltage, for example volts, and atleast one higher line voltage, for example 220, 380, 440 and 480 volts,and with fixed or adjustable taps, partly for means, for example forother transformers which feed the X-ray tube with filament current andhigh tension, partly for the auxiliary devices of the installation suchas relays and oil pump, and of the kind having an inner and an outerwinding, both substantially uniformly distributed on an annular ironcore, and in which the outer winding is accessible by means of at leastone adjustable tap, for example a sliding contact resting against astripped part of the outer winding or against a number of tapsdistributed along this winding, the outer winding being by means ofanother tap divided into two winding sections, of which the first onehas a substantially larger number of windings than the other windingsection, characterized in that the other winding section consists of ablindly terminated winding projecting from the other tap, the innerwinding having a number p-j-l winding sections the ends of which lead toouter terminals and of which at least the p winding sections each have anumber n of turns equal to the number of turns in the first windingsection of the outer Winding, whereas a winding section No. 1+1 islocated at one end of the inner winding and has a number of turns equalto n times the ratio between the difference of the two highest linevoltages and the lowest line voltage.

2. An adjustable transformer as claimed in claim 1, characterized inthat the first winding section of the outer winding is provided with anextra winding projecting from such end of the outer winding as islocated'at the greatest distance of the other tap, other slidingcontacts being provided on the turns of the outer winding near the othertap and near the said end of the outer windings, the said slidingcontacts resting in contact with stripped parts of the outer winding,and being mechanically coupled in such manner that they are capable ofturning simultaneously in the same direction in relation to thecircumference of the outer winding about that of the axes of symmetry ofthe iron core which is disposed at right angles to the plane of movementof the sliding contacts.

No references cited.

